Optical filter

ABSTRACT

A bandpass filter may include a set of layers. The set of layers may include a first subset of layers. The first subset of layers may include hydrogenated germanium (Ge:H) with a first refractive index. The set of layers may include a second subset of layers. The second subset of layers may include a material with a second refractive index. The second refractive index may be less than the first refractive index.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/371,692, filed Apr. 1, 2019 (now U.S. Pat. No. 10,901,127), which isa continuation of U.S. patent application Ser. No. 15/657,515, filedJul. 24, 2017 (now U.S. Pat. No. 10,247,865), which are incorporatedherein by reference.

BACKGROUND

An optical sensor device may be utilized to capture information. Forexample, the optical sensor device may capture information relating to aset of electromagnetic frequencies. The optical sensor device mayinclude a set of sensor elements (e.g., optical sensors, spectralsensors, and/or image sensors) that capture the information. Forexample, an array of sensor elements may be utilized to captureinformation relating to multiple frequencies. In one example, an arrayof sensor elements may be utilized to capture information regarding aparticular spectral range, such as a spectral range of fromapproximately 1100 nanometers (nm) to approximately 2000 nm, anotherspectral range with a center wavelength of approximately 1550 nm, or thelike. A sensor element, of the sensor element array, may be associatedwith a filter. The filter may include a passband associated with a firstspectral range of light that is passed to the sensor element. The filtermay be associated with blocking a second spectral range of light frombeing passed to the sensor element.

SUMMARY

According to some possible implementations, a bandpass filter mayinclude a set of layers. The set of layers may include a first subset oflayers. The first subset of layers may include hydrogenated germanium(Ge:H) with a first refractive index. The set of layers may include asecond subset of layers. The second subset of layers may include amaterial with a second refractive index. The second refractive index maybe less than the first refractive index.

According to some possible implementations, an optical filter mayinclude a substrate. The optical filter may include a set of alternatinghigh refractive index layers and low refractive index layers disposedonto the substrate to filter incident light. The optical filter may beconfigured to pass a first portion of the incident light within aspectral range with a center wavelength of approximately 1550 nanometers(nm) and reflect a second portion of incident light not within thespectral range. The high refractive index layers may be hydrogenatedgermanium (Ge:H). The low refractive index layers may be silicon dioxide(SiO₂).

According to some possible implementations, an optical system mayinclude an optical filter configured to filter an input optical signaland provide the filtered input optical signal. The input optical signalmay include light from a first optical source and light from a secondoptical source. The optical filter may include a set of dielectric thinfilm layers. The set of dielectric thin film layers may include a firstsubset of layers of hydrogenated germanium with a first refractiveindex. The set of dielectric thin film layers may include a secondsubset of layers of a material with a second refractive index less thanthe first refractive index. The filtered input optical signal mayinclude a reduced intensity of light from the second optical sourcerelative to the input optical signal. The optical system may include anoptical sensor configured to receive the filtered input optical signaland provide an output electrical signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are diagrams of an overview of an example implementationdescribed herein;

FIG. 2 is a diagram of a hydrogenated germanium based optical filterdescribed herein;

FIG. 3 is a diagram of a system for manufacturing a hydrogenatedgermanium based optical filter described herein;

FIGS. 4A-4D are diagrams of characteristics relating to a hydrogenatedgermanium based optical filter described herein; and

FIGS. 5A-5C are diagrams of characteristics relating to a hydrogenatedgermanium based optical filter described herein.

DETAILED DESCRIPTION

The following detailed description of example implementations refers tothe accompanying drawings. The same reference numbers in differentdrawings may identify the same or similar elements.

An optical sensor device may include a sensor element array of sensorelements to receive light initiating from an optical source, such as anoptical transmitter, a light bulb, an ambient light source, or the like.The optical sensor device may utilize one or more sensor technologies,such as a complementary metal-oxide-semiconductor (CMOS) technology, acharge-coupled device (CCD) technology, or the like. A sensor element(e.g., an optical sensor), of the optical sensor device, may obtaininformation (e.g., spectral data) regarding a set of electromagneticfrequencies. The sensor element may be an indium-gallium-arsenide(InGaAs) based sensor element, a silicon germanium (SiGe) based sensorelement, or the like.

A sensor element may be associated with a filter that filters light tothe sensor element to enable the sensor element to obtain informationregarding a particular spectral range of electromagnetic frequencies.For example, the sensor element may be aligned with a filter with apassband in a spectral range of approximately 1100 nanometers (nm) toapproximately 2000 nm, a spectral range of approximately 1500 nm toapproximately 1600 nm, a spectral range with a center wavelength ofapproximately 1550 nm, or the like to cause a portion of light that isdirected toward the sensor element to be filtered. A filter may includesets of dielectric layers to filter the portion of the light. Forexample, a filter may include dielectric filter stacks of alternatinghigh index layers and low index layers, such as alternating layers ofhydrogenated silicon (Si:H or SiH) or germanium (Ge) as a high indexmaterial and silicon dioxide (SiO₂) as a low index material. However,use of hydrogenated silicon as a high index material for a filterassociated with a spectral range with a center wavelength centered atapproximately 1550 nm may result in an excessive angle shift (e.g., anangle shift greater than a threshold). Moreover, use of germanium as ahigh index material may result in less than a threshold transmissivityfor the passband centered at approximately 1550 nm, such as atransmissivity of less than approximate 20% at a wavelength ofapproximately 1550 nm.

Some implementations, described herein, provide an optical filter withhydrogenated germanium (Ge:H or GeH) as a high index material, therebyresulting in an angle-shift that is less than a threshold. For example,an optical filter may include one or more layers of hydrogenatedgermanium or annealed hydrogenated germanium and one or more layers ofsilicon dioxide to provide, for a passband centered at a wavelength ofapproximately 1550 nm, an angle shift of less than approximately 100 nmat an angle of incidence of 45 degrees, less than approximately 30 nm atan angle of incidence of 30 degrees, less than approximately 10 nm at anangle of incidence of 15 degrees, or the like. Moreover, the opticalfilter using hydrogenated germanium and/or annealed hydrogenatedgermanium may provide greater than a threshold level of transmissivityfor a passband centered at approximately 1550 nm, such as atransmissivity greater than approximately 40%, greater thanapproximately 80%, greater than approximately 85%, or the like. In thisway, some implementations described herein filter light with less than athreshold angle shift and with greater than a threshold level oftransmission.

FIGS. 1A-1C are diagrams of an overview of example implementations100/100′/100″ described herein. As shown in FIG. 1A, exampleimplementation 100 includes a sensor system 110. Sensor system 110 maybe a portion of an optical system, and may provide an electrical outputcorresponding to a sensor determination. Sensor system 110 includes anoptical filter structure 120, which includes an optical filter 130, andan optical sensor 140. For example, optical filter structure 120 mayinclude an optical filter 130 that performs a passband filteringfunctionality. In another example, an optical filter 130 may be alignedto an array of sensor elements of optical sensor 140.

Although some implementations, described herein, may be described interms of an optical filter in a sensor system, implementations describedherein may be used in another type of system, may be used external to asensor system, or the like.

As further shown in FIG. 1A, and by reference number 150, an inputoptical signal is directed toward optical filter structure 120. Theinput optical signal may include but is not limited to light associatedwith a particular spectral range (e.g., a spectral range centered atapproximately 1550 nm), such as a spectral range of 1500 nm to 1600 nm,a spectral range of 1100 nm to 2000 nm, or the like. For example, anoptical transmitter may direct the light toward optical sensor 140 topermit optical sensor 140 to perform a measurement of the light. Inanother example, the optical transmitter may direct another spectralrange of light for another functionality, such as a testingfunctionality, a sensing functionality, a communications functionality,or the like.

As further shown in FIG. 1A, and by reference number 160, a firstportion of the optical signal with a first spectral range is not passedthrough by optical filter 130 and optical filter structure 120. Forexample, dielectric filter stacks of dielectric thin film layers, whichmay include high index material layers and low index material layers ofoptical filter 130, may cause the first portion of light to be reflectedin a first direction, to be absorbed, or the like. In this case, thefirst portion of light may be a threshold portion of light incident onoptical filter 130 not included in a bandpass of optical filter 130,such as greater than 95% of light not within a particular spectral rangecentered at approximately 1550 nm. As shown by reference number 170, asecond portion of the optical signal is passed through by optical filter130 and optical filter structure 120. For example, optical filter 130may pass through the second portion of light with a second spectralrange in a second direction toward optical sensor 140. In this case, thesecond portion of light may be a threshold portion of light incident onoptical filter 130 within a bandpass of optical filter 130, such asgreater than 50% of incident light in a spectral range centered atapproximately 1550 nm.

As further shown in FIG. 1A, based on the second portion of the opticalsignal being passed to optical sensor 140, optical sensor 140 mayprovide an output electrical signal 180 for sensor system 110, such asfor use in imaging, ambient light sensing, detecting the presence of anobject, performing a measurement, facilitating communication, or thelike. In some implementations, another arrangement of optical filter 130and optical sensor 140 may be utilized. For example, rather than passingthe second portion of the optical signal collinearly with the inputoptical signal, optical filter 130 may direct the second portion of theoptical signal in another direction toward a differently located opticalsensor 140.

As shown in FIG. 1B, another example implementation 100′ includes a setof sensor elements of a sensor element array forming optical sensor 140and integrated into a substrate of optical filter structure 120. In thiscase, optical filter 130 is disposed directly onto the substrate. Inputoptical signals 150-1 and 150-2 are received at multiple differentangles and first portions 160-1 and 160-2 of input optical signals 150-1and 150-2 are reflected at multiple different angles. In this case,second portions of input optical signals 150-1 and 150-2 are passedthrough optical filter 130 to a sensor element array forming opticalsensor 140, which provides an output electrical signal 180.

As shown in FIG. 1C, another example implementation 100″ includes a setof sensor elements of a sensor element array forming optical sensor 140and separated from an optical filter structure 120 (e.g., by free spacein a free space optics type of optical system). In this case, opticalfilter 130 is disposed onto optical filter structure 120. Input opticalsignals 150-1 and 150-2 are received at multiple different angles atoptical filter 130. First portions 160-1 and 160-2 of the input opticalsignals 150-1 and 150-2 are reflected and second portions 170-1 and170-2 of the input optical signals 150-1 and 150-2 are passed by opticalfilter 130 and optical filter structure 120. Based on receiving secondportions 170-1 and 170-2, the sensor element array provides an outputelectrical signal 180.

As indicated above, FIGS. 1A-1C are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 1A-1C.

FIG. 2 is a diagram of an example optical filter 200. FIG. 2 shows anexample stackup of an optical filter using hydrogenated germanium as ahigh index material. As further shown in FIG. 2 , optical filter 200includes an optical filter coating portion 210 and a substrate 220.

Optical filter coating portion 210 includes a set of optical filterlayers. For example, optical filter coating portion 210 includes a firstset of layers 230-1 through 230-N (N≥1) (e.g., high refractive indexlayers (H layers)) and a second set of layers 240-1 through 240-(N+1)(e.g., low refractive index layers (L layers)). In some implementations,layers 230 and 240 may be arranged in a particular order, such as an(H-L)_(m) (m≥1) order, an (H-L)_(m)-H order, an (L-H)_(m) order, anL-(H-L)_(m) order, or the like. For example, as shown, layers 230 and240 are positioned in an (H-L)_(n)-H order with an H layer disposed at asurface of optical filter 200 and an H layer contiguous to a surface ofsubstrate 220. In some implementations, one or more other layers may beincluded in optical filter 200, such as one or more protective layers,one or more layers to provide one or more other filteringfunctionalities (e.g., a blocker, an anti-reflection coating, etc.), orthe like.

Layers 230 may include a set of hydrogenated germanium layers. In someimplementations, another material may be utilized for the H layers, suchas another material with a refractive index greater than the refractiveindex of the L layers, a refractive index greater than 2.0, a refractiveindex greater than 3.0, a refractive index greater than 4.0, arefractive index greater than 4.5, a refractive index greater the 4.6,or the like, over a particular spectral range (e.g., the spectral rangeof approximately 1100 nm to approximately 2000 nm, the spectral range ofapproximately 1400 nm to approximately 1600 nm, the wavelength ofapproximately 1550 nm, or the like). In another example, layers 230 maybe selected to include a refractive index of approximately 4.2 at awavelength of approximately 1550 nm.

In some implementations, a particular hydrogenated germanium basedmaterial may be selected for the H layers 230, such as hydrogenatedgermanium, annealed hydrogenated germanium, or the like. In someimplementations, layers 230 and/or 240 may be associated with aparticular extinction coefficient, such as an extinction coefficient, atapproximately 1550 nm, of less than approximately 0.1, less thanapproximately 0.05, less than approximately 0.01, less thanapproximately 0.005, an extinction coefficient of less thanapproximately 0.001, an extinction coefficient of less thanapproximately 0.0008, or the like over a particular spectral range(e.g., the spectral range of approximately 800 nm to approximately 2300nm, the spectral range of approximately 1100 nm to approximately 2000nm, the wavelength of approximately 1550 nm, or the like).

Layers 240 may include a set of layers silicon dioxide (SiO₂) layers. Insome implementations, another material may be utilized for the L layers.In some implementations, a particular material may be selected for Llayers 240. For example, layers 240 may include a set of silicon dioxide(SiO₂) layers, a set of aluminum oxide (Al₂O₃) layers, a set of titaniumdioxide (TiO₂) layers, a set of niobium pentoxide (Nb₂O₅) layers, a setof tantalum pentoxide (Ta₂O₅) layers, a set of magnesium fluoride (MgF₂)layers, or the like. In this case, layers 240 may be selected to includea refractive index lower than that of the layers 230 over, for example,a particular spectral range (e.g., the spectral range of approximately1100 nm to approximately 2000 nm, the spectral range of approximately1400 nm to approximately 1600 nm, the wavelength of approximately 1550nm, or the like). For example, layers 240 may be selected to beassociated with a refractive index of less than 3 over a particularspectral range (e.g., the spectral range of approximately 1100 nm toapproximately 2000 nm, the spectral range of approximately 1400 nm toapproximately 1600 nm, a spectral range of approximately 800 nm, thewavelength of approximately 1550 nm, or the like).

In another example, layers 240 may be selected to be associated with arefractive index of less than 2.5 over a particular spectral range(e.g., the spectral range of approximately 1100 nm to approximately 2000nm, the spectral range of approximately 1400 nm to approximately 1600nm, the wavelength of approximately 1550 nm, or the like). In anotherexample, layers 240 may be selected to be associated with a refractiveindex of less than 2 over a particular spectral range (e.g., thespectral range of approximately 1100 nm to approximately 2000 nm, thespectral range of approximately 1400 nm to approximately 1600 nm, thewavelength of approximately 1550 nm, or the like). In another example,layers 240 may be selected to be associated with a refractive index ofless than 1.5 over a particular spectral range (e.g., the spectral rangeof approximately 1100 nm to approximately 2000 nm, the spectral range ofapproximately 1400 nm to approximately 1600 nm, the wavelength ofapproximately 1550 nm, or the like). In some implementations, theparticular material may be selected for layers 240 based on a desiredwidth of an out-of-band blocking spectral range, a desiredcenter-wavelength shift associated with a change of angle of incidence,or the like.

In some implementations, optical filter coating portion 210 may beassociated with a particular quantity of layers, m. For example, ahydrogenated germanium based optical filter may include approximately 20layers of alternating H layers and L layers. In another example, opticalfilter 200 may be associated with another quantity of layers, such as arange of 2 layers to 1000 layers, a range of 4 to 50 layers, or thelike. In some implementations, each layer of optical filter coatingportion 210 may be associated with a particular thickness. For example,layers 230 and 240 may each be associated with a thickness of betweenapproximately 5 nm and approximately 2000 nm, resulting in opticalfilter coating portion 210 being associated with a thickness of betweenapproximately 0.2 μm and 100 μm, a thickness of between approximately0.5 μm and 20 μm, or the like.

In some implementations, layers 230 and 240 may be associated withmultiple thicknesses, such as a first thickness for layers 230 and asecond thickness for layers 240, a first thickness for a first subset oflayers 230 and a second thickness for a second subset of layers 230, afirst thickness for a first subset of layers 240 and a second thicknessfor a second subset of layers 240, or the like. In this case, a layerthickness and/or a quantity of layers may be selected based on anintended set of optical characteristics, such as an intended passband,an intended transmissivity, or the like. For example, the layerthickness and/or the quantity of layers may be selected to permitoptical filter 200 to be utilized for a spectral range of approximately1100 nm to approximately 2000 nm, at a center wavelength ofapproximately 1550 nm, or the like.

In some implementations, optical filter coating portion 210 may befabricated using a sputtering procedure. For example, optical filtercoating portion 210 may be fabricated using a pulsed-magnetron basedsputtering procedure to sputter alternating layers 230 and 240 on aglass substrate. In some implementations, optical filter coating portion210 may be associated with a relatively low center-wavelength shift withchange in angle of incidence. For example, optical filter coatingportion 210 may cause a center-wavelength shift of less thanapproximately 20 nm, less than approximately 15 nm, less thanapproximately 10 nm, or the like in magnitude with a change in incidenceangle from 0 degrees to 15 degrees; a center-wavelength shift of lessthan approximately 100 nm, less than approximately 50 nm, less thanapproximately 30 nm, or the like with a change in incidence angle from 0degrees to 30 degrees; a center-wavelength shift of less thanapproximately 200 nm, less than approximately 150 nm, less thanapproximately 125 nm, less than approximately 100 nm, or the like with achange in incidence angle from 0 degrees to 45 degrees; or the like.

In some implementations, optical filter coating portion 210 is attachedto a substrate, such as substrate 220. For example, optical filtercoating portion 210 may be attached to a glass substrate. In someimplementations, optical filter coating portion 210 may be associatedwith an incident medium, such as an air medium or glass medium. In someimplementations, optical filter 200 may be disposed between a set ofprisms.

In some implementations, an annealing procedure may be utilized tofabricate optical filter coating portion 210. For example, after sputterdeposition of layers 230 and 240 on a substrate, optical filter 200 maybe annealed to improve one or more optical characteristics of opticalfilter 200, such as reducing an absorption coefficient of optical filter200 relative to another optical filter for which an annealing procedureis not performed.

As indicated above, FIG. 2 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 2 .

FIG. 3 is diagram of an example 300 of a sputter deposition system formanufacturing a hydrogenated germanium based optical filter describedherein.

As shown in FIG. 3 , example 300 includes a vacuum chamber 310, asubstrate 320, a cathode 330, a target 331, a cathode power supply 340,an anode 350, a plasma activation source (PAS) 360, and a PAS powersupply 370. Target 331 may include a germanium material. PAS powersupply 370 may be utilized to power PAS 360 and may include a radiofrequency (RF) power supply. Cathode power supply 340 may be utilized topower cathode 330 and may include a pulsed direct current (DC) powersupply.

With regard to FIG. 3 , target 331 is sputtered in the presence ofhydrogen (H₂), as well as an inert gas, such as argon, to deposit ahydrogenated germanium material as a layer on substrate 320. The inertgas may be provided into the chamber via anode 350 and/or PAS 360.Hydrogen is introduced into the vacuum chamber 310 through PAS 360,which serves to activate the hydrogen. Additionally, or alternatively,cathode 330 may cause hydrogen activation (e.g., in this case, hydrogenmay be introduced from another part of vacuum chamber 310) or anode 350may cause hydrogen activation (e.g., in this case, hydrogen may beintroduced into vacuum chamber 310 by anode 350). In someimplementations, the hydrogen may take the form of hydrogen gas, amixture of hydrogen gas and a noble gas (e.g., argon gas), or the like.PAS 360 may be located within a threshold proximity of cathode 330,allowing plasma from PAS 360 and plasma from cathode 330 to overlap. Theuse of the PAS 360 allows the hydrogenated germanium layer to bedeposited at a relatively high deposition rate. In some implementations,the hydrogenated germanium layer is deposited at a deposition rate ofapproximately 0.05 nm/s to approximately 2.0 nm/s, at a deposition rateof approximately 0.5 nm/s to approximately 1.2 nm/s, at a depositionrate of approximately 0.8 nm/s, or the like.

Although the sputtering procedure is described, herein, in terms of aparticular geometry and a particular implementation, other geometriesand other implementations are possible. For example, hydrogen may beinjected from another direction, from a gas manifold in a thresholdproximity to cathode 330, or the like. Although, described, herein, interms of different configurations of components, different relativeconcentrations of germanium may also be achieved using differentmaterials, different manufacturing processes, or the like.

As indicated above, FIG. 3 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 3 .

FIGS. 4A-4D show examples relating to optical filters using hydrogenatedgermanium as a high index material. FIGS. 4A-4D show characteristicsrelating to hydrogenated germanium based single layer films.

As shown in FIG. 4A, and by chart 400, a filter response showingtransmissivity for a set of films 410-1 through 410-5 is provided. Eachfilm 410 may be an approximately 2.5 micrometer single layer film. Film410-1 is associated with a concentration of hydrogen associated with aflow rate of 0 standard cubic centimeters per minute (SCCM). In otherwords, film 410-1 uses non-hydrogenated germanium. Films 410-2, 410-3,410-4, and 410-5 are associated with concentrations of hydrogenassociated with flow rates of 20 SCCM, 100 SCCM, 160 SCCM, and 200 SCCM.In other words, films 410-2 through 410-5 use hydrogenated germaniumwith increasing concentrations of hydrogen. In this case, thehydrogenated germanium films, such as films 410-2 through 410-5, areassociated with increased transmissivity relative to non-hydrogenatedgermanium film 410-1. In this way, utilizing hydrogenated germanium inan optical filter can provide improved transmissivity. For example,based on a concentration of hydrogen in a hydrogenated germanium film, ahydrogenated germanium film may be associated with as a transmissivitygreater than 20%, greater than 40%, greater than 60%, greater than 80%,greater than 85%, greater than 90%, or the like for a spectral range of1100 nm to 2000 nm, a spectral range of 1400 nm to 1600 nm, a spectralrange with a wavelength of 1550 nm, or the like.

As shown in FIG. 4B, and by chart 420, an index of refraction and anextinction coefficient for the films 410 are provided. At a wavelengthof 1400 nm, non-hydrogenated germanium film 410-1 is associated with anextinction coefficient of approximately 0.1, which is greater than theextinction coefficients for hydrogenated germanium films 410-2, 410-3,and 410-5, which are approximately 0.05, approximately 0.005, andapproximately 0.002, respectively. Similarly, at a wavelength of 1400nm, non-hydrogenated germanium film 410-1 is associated with arefractive index of 4.7, which compares with hydrogenated germaniumfilms 410-2, 410-3, and 410-5, which are associated with refractiveindices of 4.6, 4.4 and 4.3, respectively. In this case,hydrogenated-germanium films 410-2, 410-3, and 410-5 are associated witha reduced extinction coefficient while maintaining a thresholdrefractive index (e.g., greater than 4.0, greater than 4.2, greater than4.4, greater than 4.5, etc.).

At a wavelength of 1550 nm, non-hydrogenated germanium film 410-1 isassociated with an extinction coefficient of approximately 0.07, whichis greater than the extinction coefficients for hydrogenated germaniumfilms 410-2, 410-3, and 410-5, which are approximately 0.03,approximately 0.003, and approximately 0.001, respectively. Similarly,at a wavelength of 1550 nm, non-hydrogenated germanium film 410-1 isassociated with a refractive index of 4.6, which compares withhydrogenated germanium films 410-2, 410-3, and 410-5, which areassociated with refractive indices of 4.4, 4.3 and 4.2, respectively. Inthis case, hydrogenated-germanium films 410-2, 410-3, and 410-5 areassociated with a reduced extinction coefficient while maintaining athreshold refractive index (e.g., greater than 4.0, greater than 4.2,greater than 4.4, etc.).

At a wavelength of 2000 nm, non-hydrogenated germanium film 410-1 isassociated with an extinction coefficient of approximately 0.05, whichis greater than the extinction coefficients for hydrogenated germaniumfilms 410-2, 410-3, and 410-5, which are approximately 0.005,approximately 0.0005, and approximately 0.000001, respectively.Similarly, at a wavelength of 1550 nm, non-hydrogenated germanium film410-1 is associated with a refractive index of 4.5, which compares withhydrogenated germanium films 410-2, 410-3, and 410-5, which areassociated with refractive indices of 4.4, 4.2 and 4.1, respectively. Inthis case, hydrogenated-germanium films 410-2, 410-3, and 410-5 areassociated with a reduced extinction coefficient while maintaining athreshold refractive index (e.g., greater than 3.5, greater than 3.75,greater than 4.0).

As shown in FIG. 4C, and by chart 430, an index of refraction forhydrogenated germanium film 410-5 and a hydrogenated silicon film 410-6is provided. In this case, the index of refraction for hydrogenatedgermanium film 410-5 is each greater than an index of refraction forhydrogenated silicon film 410-6.

As shown in FIG. 4D, and by chart 440, an index of refraction and anextinction coefficient are provided for hydrogenated germanium film410-5 and an annealed hydrogenated germanium film 410-5′. In this case,applying an annealing procedure, for example, at approximately 300degrees Celsius for 60 minutes results in forming annealed hydrogenatedgermanium film 410-5′, results in an increased index of refraction(e.g., increased to approximately 4.3) and a reduced extinctioncoefficient (e.g., reduced to approximately 0.0006) at a spectral rangewith a center wavelength of approximately 1550 nm relative tohydrogenated germanium film 410-5, thereby reducing angle shift andimproving transmissivity.

As indicated above, FIGS. 4A-4D are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 4A-4D.

FIGS. 5A-5C are diagrams of characteristics relating to an opticalfilter. FIGS. 5A-5C show characteristics relating to bandpass filters.

As shown in FIG. 5A, and by chart 500, a filter response is provided fora hydrogenated germanium optical filter 510. Optical filter 510 mayinclude alternating layers of hydrogenated germanium and silicondioxide. In some implementations, optical filter 510 may be associatedwith a thickness of approximately 5.6 μm, and may be associated with abandpass centered at approximately 1550 nm for an angle of incidence of0 degrees. Moreover, optical filter 510 is associated with atransmissivity of greater than a threshold amount (e.g., greater thanapproximately 90%) for angles of incidence from 0 degrees to 40 degrees.

As shown in FIG. 5B, and by chart 520, a filter response is provided fora hydrogenated silicon based optical filter 530. Optical filter 530 mayinclude alternating layers of hydrogenated silicon and silicon dioxide.In some implementations, optical filter 530 may be associated with athickness of approximately 5.9 micrometers (μm) and may be associatedwith a bandpass centered at approximately 1550 nm for an angle ofincidence of 0 degrees.

As shown in FIG. 5C, and by chart 540, relative to optical filter 510(Si:Ge), optical filter 530 (Si:H) is associated with a reduced angleshift for changes of angles of incidence from 0 degrees to approximately40 degrees. For example, optical filter 510 is associated with a changein center wavelength of, for example, less than approximately 5 nm at anangle of incidence of approximately 0-10 degrees, less thanapproximately 4 nm at an angle of incidence of approximately 0-10degrees, less than approximately 3 nm at an angle of incidence ofapproximately 0-10 degrees, less than approximately 2 nm at an angle ofincidence of approximately 0-10 degrees, or the like. Similarly, opticalfilter 510 is associated with a change in center wavelength of, forexample, less than approximately 15 nm at an angle of incidence of 10-20degrees, less than approximately 10 nm at an angle of incidence of 10-20degrees, less than approximately 9 nm at an angle of incidence of 10-20degrees, less than approximately 8 nm at an angle of incidence of 10-20degrees, or the like.

Similarly, optical filter 510 is associated with a change in centerwavelength of, for example, less than approximately 8 nm at an angle ofincidence of 20 degrees, less than approximately 9 nm at an angle ofincidence of 20 degrees, less than approximately 30 nm at an angle ofincidence of 20-30 degrees, less than approximately 20 nm at an angle ofincidence of 20-30 degrees, less than approximately 15 nm at an angle ofincidence of 20-30 degrees, less than approximately 10 nm at an angle ofincidence of 20-30 degrees, or the like. Similarly, optical filter 510is associated with a change in center wavelength of, for example, lessthan approximately 40 nm at an angle of incidence of approximately 30-40degrees, less than approximately 35 nm at an angle of incidence ofapproximately 30-40 degrees, less than approximately 30 nm at an angleof incidence of approximately 30-40 degrees, less than approximately 25nm at an angle of incidence of approximately 30-40 degrees, less thanapproximately 20 nm at an angle of incidence of approximately 30-40degrees, or the like.

As indicated above, FIGS. 5A-5C are provided merely as examples. Otherexamples are possible and may differ from what was described with regardto FIGS. 5A-5C.

In this way, a hydrogenated germanium optical filter, such as an opticalfilter with hydrogenated germanium as a high index layer and anothermaterial as a low index layer, may provide improved angel shift,improved transmissivity, and reduced physical thickness relative toother materials for an optical filter associated with a spectral rangewith a center wavelength at approximately 1550 nm.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the implementations to theprecise form disclosed. Modifications and variations are possible inlight of the above disclosure or may be acquired from practice of theimplementations.

Some implementations are described herein in connection with thresholds.As used herein, satisfying a threshold may refer to a value beinggreater than the threshold, more than the threshold, higher than thethreshold, greater than or equal to the threshold, less than thethreshold, fewer than the threshold, lower than the threshold, less thanor equal to the threshold, equal to the threshold, etc.

Even though particular combinations of features are recited in theclaims and/or disclosed in the specification, these combinations are notintended to limit the disclosure of possible implementations. In fact,many of these features may be combined in ways not specifically recitedin the claims and/or disclosed in the specification. Although eachdependent claim listed below may directly depend on only one claim, thedisclosure of possible implementations includes each dependent claim incombination with every other claim in the claim set.

No element, act, or instruction used herein should be construed ascritical or essential unless explicitly described as such. Also, as usedherein, the articles “a” and “an” are intended to include one or moreitems, and may be used interchangeably with “one or more.” Furthermore,as used herein, the term “set” is intended to include one or more items(e.g., related items, unrelated items, a combination of related items,and unrelated items, etc.), and may be used interchangeably with “one ormore.” Where only one item is intended, the term “one” or similarlanguage is used. Also, as used herein, the terms “has,” “have,”“having,” or the like are intended to be open-ended terms. Further, thephrase “based on” is intended to mean “based, at least in part, on”unless explicitly stated otherwise.

What is claimed is:
 1. An optical filter, comprising: one or more firstlayers, and one or more second layers, wherein the one or more firstlayers and the one or more second layers are configured to provide anangle shift of less than approximately 100 nanometers (nm) at an angleof incidence of 45 degrees or less than approximately 30 nm at an angleof incidence of 30 degrees, and wherein the one or more first layersinclude one or more layers of annealed hydrogenated germanium.
 2. Theoptical filter of claim 1, wherein the one or more first layers furtherinclude one or more layers of hydrogenated germanium.
 3. The opticalfilter of claim 1, wherein the one or more second layers include one ormore layers of silicon dioxide.
 4. The optical filter of claim 1,wherein the one or more first layers provide a transmissivity greaterthan approximately 40% for a passband centered at a wavelength ofapproximately 1550 nm.
 5. The optical filter of claim 1, wherein the oneor more first layers are further configured to provide a transmissivitygreater than approximately 80% for a passband centered at a wavelengthof approximately 1550 nm.
 6. The optical filter of claim 1, wherein theone or more first layers are further configured to provide atransmissivity greater than approximately 85% for a passband centered ata wavelength of approximately 1550 nm.
 7. The optical filter of claim 1,wherein the one or more first layers and the one or more second layersare configured to provide the angle shift of less than approximately 100nm at the angle of incidence of 45 degrees or less than approximately 30nm at the angle of incidence of 30 degrees for a passband centered at awavelength of approximately 1550 nm.
 8. An optical filter, comprising:one or more first layers with a first refractive index, the one or morefirst layers comprising a hydrogenated germanium film with an extinctioncoefficient of less than 0.001 at a spectral range with a centerwavelength of approximately 1550 nanometers (nm), and the hydrogenatedgermanium film being an annealed hydrogenated germanium film; and one ormore second layers with a second refractive index.
 9. The optical filterof claim 8, wherein the second refractive index is less than the firstrefractive index.
 10. The optical filter of claim 8, wherein theextinction coefficient is approximately 0.0006.
 11. The optical filterof claim 8, wherein the hydrogenated germanium film has an index ofrefraction of approximately 4.3.
 12. The optical filter of claim 8,wherein the hydrogenated germanium film is an approximately 2.5micrometer single layer film.
 13. The optical filter of claim 8, whereinthe one or more first layers further comprise a non-hydrogenatedgermanium film.
 14. The optical filter of claim 13, wherein thenon-hydrogenated germanium film is associated with an extinctioncoefficient of approximately 0.07 and a refractive index of 4.6 at thespectral range with the center wavelength of approximately 1550 nm. 15.The optical filter of claim 8, wherein the one or more first layersfurther comprise one or more other hydrogenated germanium films.
 16. Theoptical filter of claim 8, wherein the hydrogenated germanium film isassociated with a refractive index of less than 4.6 at the spectralrange with the center wavelength of approximately 1550 nm.
 17. Theoptical filter of claim 8, wherein the one or more second layers includeone or more of: a silicon dioxide (SiO2) material, an aluminum oxide(Al2O3) material, a titanium dioxide (TiO2) material, a niobiumpentoxide (Nb2O5) material, a tantalum pentoxide (Ta2O5) material, or amagnesium fluoride (MgF2) material.
 18. An optical filter, comprising: afirst set of layers comprising: a non-hydrogenated germanium film; oneor more hydrogenated germanium films; and an annealed hydrogenatedgermanium film; and a second set of layers.
 19. The optical filter ofclaim 18, wherein the annealed hydrogenated germanium film is associatedwith an extinction coefficient of less than 0.0001 at a spectral rangewith a center wavelength of approximately 1550 nanometers (nm).
 20. Theoptical filter of claim 18, wherein the second set of layers include oneor more layers of silicon dioxide.